This invention is related to a computer-operated process for graphically determining whether the average thickness of individual or multiple layers of a multi-layer coating detected by a Pelt Gage at a plurality of spaced locations on several workpieces considering selected parameters, are within the range of acceptable thickness.
A Pelt Gage (pulse/echo layer thickness Gage) is a computer controlled ultra-sonic coating layer thickness measurement system. The Pelt Gage is used in industrial applications to measure the thickness of multiple layers of coatings on either metallic or plastic substrates. The Pelt Gage initiates a thickness measurement by generating a very short electrical pulse. An ultra-sonic transducer converts this electrical pulse to a mechanical or acoustic pulse. The transducer is acoustically coupled to the sample being measured so that an appreciable portion of the pulse energy is transmitted into the sample coating layers. As the acoustic pulse propagates through the coating layers, reflections or echoes are produced each time the pulse crosses the boundary between layers. The amount of energy reflected back at the interface between two coatings or materials is related to the difference in the acoustic properties of the materials.
The Pelt Gage measures layer thickness by precisely determining the time differences between successive layer boundary reflections and multiplying these time differences by the calibrated sound velocities for each coating layer. Pelt Gages are commonly used in industrial applications, such as for measuring the thickness of a multi-layer coating on automotive bodies for quality assurance purposes. Pelt Gages are available from JSR Ultrasonic of Pittsford, N.Y.
In the automotive industry, the thickness of the coating on sample vehicle bodies is measured to determine deviations in the coating process. For example, in a typical plant, three cars out of 1000 cars produced per day may be checked for coating quality. The worker takes Pelt Gage measurements at a selected number of locations on the vehicle body, for example, such as 105 spaced locations. Each vehicle body has a multi-layer coating on the metal surface. These layers usually include, a phosphate coating (not measured by the Pelt Gage); an E Coat which is a corrosion coating; a primer coating; a base coat (the color coat); and finally a clear coat. The Pelt Gage measures the thickness of four layers, entering four values for each location into the systems computer data base. The thickness measurements for all locations are then averaged for the vehicle, and for each of the four layers. Typically, the raw data as well as the averages for up to 23 vehicles are stored in a data base, over a period of several days.
The user also inputs into the data for each vehicle the plant location, the booth location in the plant, the color of the base coat, the date and the location on the vehicle of each thickness measurement. Thus, several hundred items of data are recorded and stored for each vehicle.
The information is then down loaded on a disc and the information printed to manually generate Statistical Process Control (SPC) charts to determine if the pattern or trend of selected thickness measurements are acceptable, or unacceptable. If unacceptable, the reasons for the deviation are determined and the coating equipment adjusted.
In some cases trends can only be determined by referring to a historical data base. For example, some vehicle colors are infrequent, therefore several weeks data must be searched to obtain sufficient data for trends of certain color combinations.
Once this data is presented, the manufacturing facility, if utilizing statistical controls for film thickness readings, must manually translate the data by surface area, by color, and/or color group and/or painting location and/or style of manufactured part and hand generate one or more of three statistical control charts from these readings. These control charts would either be an individual X BAR (average thickness vs. time), R CHART (range of thickness vs. time), an Individual and Moving Range Chart or an X BAR (average thickness vs. time) and S CHART (standard deviation vs. time). The labor time required to generate and maintain these charts is substantial.
Previous attempts at generating statistical control charts from Pelt Gage measurements suffer from a number of disadvantages; for example, substantial labor time must be allocated at each manufacturing facility to transcribe the Pelt Gage data and either maintain or generate a statistical control chart:
(a) of each surface area measured; PA1 (b) of each painting booth within the plant; PA1 (c) for each style of manufacturer product that is produced; PA1 (d) for each color group or individual color that is used on the painted product; PA1 (e) for each coating type that is used on the painted product; PA1 (f) for specific time frames where process improvements or evaluations are being conducted; PA1 (g) for a customized chart where process improvements or evaluations are being conducted. PA1 (a) of each surface area measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (b) of each painting location measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (c) of each style of manufacturer product measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (d) of each color group or individual color measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (e) of each coating type measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (f) of specific time frames with raw data measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (g) of process improvements or evaluations of raw data measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (h) on a timely basis with data taken by a Pelt Gage thereby identifying trends which will reduce the number of reworks; PA1 (i) of specific time frames with raw data measured with a Pelt Gage, thereby reducing labor costs and material wastes; PA1 (j) with a scaleable y-axis with raw data measured with a Pelt Gage, thereby providing easier interpretation of film build data; PA1 (k) with colored control limit lines and square marker identification with raw data measured with a Pelt Gage, thereby providing easier interpretation of film build data; PA1 (l) permitting manual insertion or calculated capabilities of history bars: A-Bar, B-Bar and control limit lines with raw data measured with a Pelt Gage, thereby providing easier interpretation of film build data; and PA1 (m) providing an autoprocess function that allows the user to print or preview all standard and/or custom charts in selected combinations with any surface area and/or style measured with raw data measured with a Pelt Gage, thereby providing easier interpretation of film build data. PA1 a) as the amount of reworks are reduced through statistical analysis, the user can reduce paint usage and the associated clean-up costs associated with this process; PA1 b) the user can avoid excessive paint reducing solvent usage and costs; and PA1 c) the user can reduce paint sludge generation, excessive paint sludge disposal costs, and excessive paint sludge transportation costs.
Substantial paint waste occurs because of the delay in identifying trends, thus resulting in excessive rework of the product.